The present invention relates, in general, to electronics, and more particularly, to semiconductors, structures thereof, and methods of forming semiconductor devices.
In the past, the semiconductor industry utilized various methods and structures to build switching power supply controllers that could be utilized in a power supply system such as in a flyback switching power supply system. In some applications, the switching power supply controllers were designed to operate in a discontinuous conduction mode and to use a value of the drain-to-source voltage across the switch transistor to determine the proper time for enabling the switch transistor. This was often referred to as a quasi-resonant operation or valley switching operation. During the operation of these power supply controllers, the switching frequency varied because the circuit kept the switch transistor disabled for a variable amount of time based on the voltage across the switch transistor. Because the frequency varied, prior controllers used different techniques to determine the proper time to re-enable the switch transistor. One particular technique sampled the frequency of oscillations there were formed by the voltage on the drain of the switch transistor and used the frequency to determine the proper time for re-enabling the switch transistor. However, this technique required complex circuitry which increased the cost of the power supply controller.
Accordingly, it is desirable to have a power supply controller that utilizes less complex circuitry, and that has a lower cost.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are reasonable variances from the ideal goal of exactly as described.